SARS-CoV-2 Antibody Detection

Although an antibody test cannot distinguish between a recent or past infection, it has an advantage over a virus detection via PCR: it can detect a SARS-CoV-2 infection well after there are no more viral particles or RNA detectable in the blood (i.e., weeks or months after the infection were over). It can also help to determine whether a vaccination were successful and/or is still active. The contents of this article have been compiled with the greatest possible care. However, please note that the current situation on SARS-CoV-2 remains very dynamic.

What are antibodies, and which antibodies are important in COVID-19? Antibodies are large proteins which are synthesized by the immune system. They are also called immunoglobulins (Ig). Each immunoglobulin binds to a specific pathogen molecule, which is called the “antigen”das Antigen. There are many different types of antibodies, each of them is responsible for different tasks in the body.

In the case of a SARS-CoV-2 infection, the first antibodies produced are of the IgA type. They are formed and found in the secretions of the mucous membranes , e.g., of the respiratory tract, in tears , saliva and the gastrointestinal and respiratory tracts (and also in breast milk and blood). At the points of entry, IgA antibodies serve primarily as a local defense of the body against pathogens. Then IgM and IgG antibodies are formed almost simultaneously after a SARS-CoV-2 infection, detectable about two weeks after infection. IgM antibodies are synthesized by B-cells. They are either present on the membrane of the B-cells or are secreted into the blood. IgG antibodies represent the majority of antibodies. They are part of the immunological memory and remain detectable in the blood for a very long time after infection. Many different IgG will “watch out” for many viral diseases.

Where are SARS-CoV-2 antibodies detected? As a rule, approximately one to three weeks elapse between the onset of symptoms and the detectability of specific antibodies (in individual cases even more). The SARS-CoV-2 specific antibodies can be detected both during the acute infection phase and after symptoms have subsided . Antibody tests are therefore not suitable for the detection of a current infection, but can complement the diagnosis, especially if two consecutive blood samples are examined and antibody time courses (IgM, IgA, IgG) are analyzed.

In addition to direct detection of SARS-CoV-2 from swab material using PCR, indirect detection using SARS-CoV-2 antibodies in serum also exists. Most immunoassays detect SARS-CoV-2 IgG. The detected antibodies are directed against different SARS-CoV-2 proteins, depending on the assay: nucleocapsid (N) or the spike protein (S). Data on specificity, sensitivity and immunity are currently the subject of various studies by the Robert Koch-Institute (RKI).

What tests are available and what are the differences between the various SARS-CoV-2 antibody detections? In the field of SARS-CoV-2 diagnostics, a comprehensive range of services is available, for both the serological diagnosis of an existing or past infection with SARS-CoV-2 and for the detection of SARS-CoV-2 antibodies after SARS-CoV-2 vaccination. There are many test options; here are just a few.

Basically, two groups of testing methods exist:

Firstly, binding antibody detection uses purified virus antigens which then bind to the antibody. This way one can identify IgA in the mucous , as well as IgG or IgM in the blood:

Point-of-care (POC) tests can be performed rapidly (within minutes) as a fast diagnosis on-site and without much lab safety and at rather low costs. Mucous swabs from the nose or mouth cavity are taken, or capillary blood collection is used.

Laboratory tests use ELISA, lateral flow or chemiluminescent immunoassays. Typically, these tests are performed in specialized labs with trained staff. They detect IgG and IgM in whole blood, serum or plasma and are very accurate.

Secondly, neutralizing antibody detection testing is a completely different approach that tests whether the patient antibodies neutralize SARS-CoV-2 (in other words: whether the produced antibodies are able to prevent an infection). These are in-vitro assays that measure the growth or survival of SARS-CoV-2 in cell culture. For example, they detect plaque reduction or pseudovirus neutralization.

Is antibody testing covered by health insurance? Currently, the costs for the determination of SARS-CoV-2 antibodies are only covered for patients with a recent symptomatic illness. However, there are currently some political negotiations that may lead to the test being covered by statutory and private health insurance in 2022.

EXERCISE: 1. It usually takes two to three weeks after SARS-CoV-2-infection for specific antibodies to be detectable.

a) True b) False

2. In Germany, the costs of antibody determinations for SARS-CoV-2 are currently covered by the statutory health insurance funds.

a) True b) False

3. The detected antibodies are directed against different SARS-CoV-2 proteins (nucleocapsid or spike protein), depending on the test.

a) True b) FalseYou’ll find the answer on the next page

BIBLIOGRAPHY 1. http://dict.leo.org. 2. www.cdc.gov. 3. www.dict.cc. 4. www.rki.de. 5. www.webster-dictionary.org.

CARMEN LOBITZ Carmen Lobitz ist freie Trainerin, Lehrerin und MTA. Sie gründete 1998 in Berlin lobitz seminare, die unter anderem Englischseminare für Health Professionals anbieten. Kontakt: mail@lobitz-seminare.de www.lobitz-seminare.de

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Lösung für Exercise: 1. A) 2. B) 3. A)

SARS-CoV-2 Antibody Detection

What are antibodies, and which antibodies are important in COVID-19?

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SARS-CoV-2 Antibody Detection

What are antibodies, and which antibodies are important in COVID-19?

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